i have asked this question many times but no one is able to help out.

Following things are done but with no good result.

1.spark plugs changed and cleaned many times.
2.throttle body and IACV valves serviced many times.
3.tappets were done as mechanic said they are loose.fixed the issue and car was weightless but engine shuts off every time the foot is taken off the accelarator so i asked mechanic to bring tappets to previous state and even after that engine was turning off so mechanic spend many hours to atleast keep engine running.
4.whole clutch plates pressure plate and bearing was changed but no difference.
5.on scanner no codes are found and if iAT code is there removing it doesnt really help.
6.fuel filter changed and so is pump changed twice but temporary solution.
7.injectors changed.

car is running on petrol but cng is installed and connections removed.

car is sluggish u have to press the throttle hard or drive like an idiot to take car to 100km/hr.
throttle body cleaning and specially IACV cleaning makes car more responsive and quick but for few days only.

another issue i would like to mention is with car rpm as it climbs to 2500 when car is started every time and often falls to 400 when the car is turned on u turns and also when car is reversed causing engine to vibrate or shut some times. cleaning IACV fixes this issue as well.

the auto civic of my friends are also weightless and when u drive it u feel that u r flying on air. mine is lazy. and sudden press of thrttle produce ghoon ghoon sound and delayed response.